Processors execute software code to perform operations. Processors may use particular software code, commonly referred to as boot code, to be executed for booting up. In a multi-processor system, each processor may use respective boot code for booting up. As an example, in a smartphone device that includes an application processor and a modem processor, each of the processors may use respective boot code for booting up.
A problem exists on a significant number of devices (such as smart phones) that incorporate multiple processors (e.g., a standalone application processor chip integrated with a separate modem processor chip). A flash/non-volatile memory component may be used for each of the processors, because each processor has non-volatile memory (e.g., persistent storage) of executable images and file systems. For instance, a processor's boot code may be stored to the processor's respective non-volatile memory (e.g., Flash memory, read-only memory (ROM), etc.), and upon power-up the boot code software is loaded for execution by the processor from its respective non-volatile memory. Thus, in this type of architecture the executable software, such as a processor's boot code, is not required to be loaded to the processor from another processor in the system.
Adding dedicated non-volatile memory to each processor, however, occupies more circuit board space, thereby increasing the circuit board size. Some designs may use a combined chip for Random Access Memory (RAM) and Flash memory (where RAM and Flash devices are stacked as one package to reduce size) to reduce board size. While multi-chip package solutions do reduce the needed circuit board foot print to some extent, it may increase costs.
In some multi-processor systems, software may be loaded to one processor from another processor. For example, suppose a first processor in a multi-processor system is responsible for storing to its non-volatile memory boot code for one or more other processors in the system; wherein upon power-up the first processor is tasked with loading the respective boot code to the other processor(s), as opposed to such boot code residing in non-volatile memory of the other processor(s). In this type of system, the software (e.g., boot image) is downloaded from the first processor to the other processor(s) (e.g., to volatile memory of the other processor(s)), and thereafter the receiving processor(s) boots with the downloaded image.
Often, the software image to be loaded is a binary multi-segmented image. For instance, the software image may include a header followed by multiple segments of code. When software images are loaded from an external device (e.g., from another processor) onto a target device (e.g., a target processor) there may be an intermediate step where the binary multi-segmented image is transferred into the system memory and then later transferred into target locations by the boot loader.
In a system in which the software image is loaded onto a target “secondary” processor from a first “primary” processor, one way of performing such loading is to allocate a temporary buffer into which each packet is received, and each packet would have associated packet header information along with the payload. The payload in this case would be the actual image data. From the temporary buffer, some of the processing may be done on the payload, and then the payload may get copied over to the final destination. The temporary buffer may be located in system memory, such as in internal random-access-memory (RAM) or double data rate (DDR) memory, for example.
Thus, where an intermediate buffer is used, the data being downloaded from a primary processor to a secondary processor is copied into the intermediate buffer. In this way, the buffer is used to receive part of the image data from the primary processor, and from the buffer the image data may be scattered into the memory (e.g., volatile memory) of the secondary processor.
The primary processor and its non-volatile memory that stores the boot image for a secondary processor may be implemented on a different chip than a chip on which the secondary processor is implemented. Thus, in order to transfer the data from the primary processor's non-volatile memory to the secondary processor (e.g., to the secondary processor's volatile memory), a packet-based communication may be employed, wherein a packet header is included in each packet communicated to the secondary processor. The packets are stored in an intermediate buffer, and some processing of the received packets is performed so that the data may be stored in its final destination (e.g., within the secondary processor's volatile memory).